In chemical processing operations, and in particular extruding of resinous materials, it may be necessary or desirable to blend additives into a viscous composition in a manner that will achieve complete and uniform mixing of the additives and the compositions. This can be a difficult objective to reach in an efficient manner where the additive has considerably less viscosity than the resinous mass, and where the mixing must take place "in-line", that is, while the composition is flowing in a production process.
In the prior art, various in-line blenders and mixers have been proposed, but in practice it has been found that they do not consistently provide a uniform blending of ingredients because of the existence of "dead" spots within the mixers through which portions of the composition can pass without intermixing thoroughly with the main body of the composition flowing through the mixer. In many instances, it is desirable to heat or cool the composition while it is mixed, but prior art apparatus has not always been compatible with good heat exchanger requirements.